Audit: rewrite audit entry formatting to improve performance

[peteski22]

Description

This PR is a bit of a re-write/refactor of the existing audit code, intended to improve performance. Various binaries/builds have been tested internally in collaboration with our Customer Engineering team to confirm the improvement on CPU, memory usage, barrier gets etc.

The 'guts' of the PR are in audit/entry_formatter.go.

Summary of larger changes:

audit/types.go

• combine RequestEntry and ResponseEntry into a single type Entry (as omitempty is set on fields it won't make a difference to the output).

audit/hashstructure.go:

• change hash funcs to accept the audit types vs. the logical ones.

audit/entry_formatter.go:

• introduce new funcs newAuth, newRequest and newResponse that can be used early to translate the incoming LogInput components into domain specific objects. These funcs will clone all the relevant parts (as opposed to the entire deep clone of the LogInput which had a significant performance impact).
• newResponse will also handle elision of the data field at the time it's about to clone which is also an improvement.
• Process method no longer performs a deep clone on the entire LogInput.
• Process has also done away with having to differentiate between a request and a response.
• We create a new eventlogger.Event as before, but we don't need to create a new AuditEvent as the only thing that matters is the (JSON/JSONx) bytes we store in the eventlogger.Event's Formatted map.
• hashing is done after creation of the Entry which will already have elided response data if required.

NOTE: Enterprise PR: https://github.com/hashicorp/vault-enterprise/pull/6373

HashiCorp Checklist

• Labels: If this PR is the CE portion of an ENT change, and that ENT change is
  getting backported to N-2, use the new style backport/ent/x.x.x+ent labels
  instead of the old style backport/x.x.x labels.
• Labels: If this PR is a CE only change, it can only be backported to N, so use
  the normal backport/x.x.x label (there should be only 1).
• ENT Breakage: If this PR either 1) removes a public function OR 2) changes the signature
  of a public function, even if that change is in a CE file, double check that
  applying the patch for this PR to the ENT repo and running tests doesn't
  break any tests. Sometimes ENT only tests rely on public functions in CE
  files.
• Jira: If this change has an associated Jira, it's referenced either
  in the PR description, commit message, or branch name.
• RFC: If this change has an associated RFC, please link it in the description.
• ENT PR: If this change has an associated ENT PR, please link it in the
  description. Also, make sure the changelog is in this PR, not in your ENT PR.

[github-actions]

CI Results:
All Go tests succeeded! ✅

[github-actions]

Build Results:
All builds succeeded! ✅

[kubawi]

LGTM